The present invention relates generally to the field of telephone call control and, in its most preferred embodiments, to the field of apparatus and methods for detecting and responding to an attempted three-way telephone call placement.
Today's modern telephone systems provide individuals and businesses with a variety of customizable telephone features and services. One of these features, known as conference or "three-way" calling, enables a telephone customer having three-way calling service (also referred to herein as the telephone call recipient or simply, the recipient) to establish a telephone connection between a telephone call originator (also referred to herein as the originator), himself (i.e., the telephone call recipient), and a third party. To establish the connection or "three-way call", the recipient receives a telephone call from the originator and subsequently places the telephone call on hold by depressing and releasing the switch hook on his telephone. Upon receiving a dial tone, the recipient dials the telephone number of the third party and establishes a connection with the third party. Then, the recipient depresses and releases his switch hook a second time to connect all three individuals.
The telephone call recipient generally receives basic telephone service and additional services, including three-way calling service, from a local telephone company having a telephone switch (also referred to herein as the recipient's end office switch) located at an end office near the location of the recipient's telephone. The recipient's end office switch connects to the recipient's telephone via, at least, a codec device (which converts signals between analog and pulse code modulated (PCM) digital forms) and a distribution network which carries analog signals between the codec device and the recipient's telephone. Similarly, the telephone call originator generally receives telephone service from a local telephone company having a telephone switch (also referred to herein as the originator's end office switch) located at an end office near the location of the originator's telephone. The recipient's telephone is similarly connected to the recipient's switch by a codec device and an analog distribution network. When the originator places a telephone call to the recipient, the originator's end office switch routes the call to the recipient's end office switch and, hence, to the recipient via, generally, digital T1 facilities which include a number of other telephone switches (including, but not limited to interchange carrier switches, access tandem switches, and other end office switches). Together, the switches, T1 facilities, codecs, and analog distribution network are referred to by those skilled in the art as the public switched network or PSN. The routing process and T1 facilities define two, one-way, digital communication paths between the originator's end office switch and the recipient's end office switch. The first communication path carries signals transmitted by the originator and received by the recipient, while the second communication path carries signals transmitted by the recipient and received by the originator.
When the telephone call recipient attempts to place a three-way call by depressing his switch hook as described above, the recipient's end office switch receives a first pulse which it transmits via the public switched telephone network along a one-way, digital communication path to the originator's telephone. After receiving the first pulse (known, in the telecommunications industry, as a switch hook request), the recipient's end office switch transmits a first period of "silence" lasting approximately 250 milliseconds to 1.2 seconds followed by a second pulse created when the recipient releases his switch hook. In combination, the first pulse, first period of silence, and second pulse are known in the telecommunicatons industry as a "hook-flash event". Similar to the first pulse, the first period of silence and second pulse are received at the originator's telephone via the one-way, digital communication path of the public switched network. In response to the depression and release of the recipient's switch hook, the recipient's end office switch suspends the telephone call and outputs a dial tone to the recipient. While the recipient dials the third party's telephone number, a second period of"silence", lasting at least 4 seconds, is observable at the originator's telephone.
While the detection of an attempted three-way call placement is of, perhaps, minor importance in many environments, the detection and response to an attempted placement of a three-way call is extremely important in the penal environment. Since prisoners often have abundant amounts of free time on their hands, inmate telephone privileges frequently provide inmates with opportunities for making nuisance calls to judges, victims, and other parties. Fortunately, some of today's telephone systems can prevent inmates from placing direct calls to parties who are previously identified to the systems by their telephone numbers. Unfortunately, many of the same telephone systems cannot prevent inmates from placing a call to a cohort "on the outside" having three-way calling service who, in turn, connects the inmate with the third party with whom the inmate wishes to talk.
U.S. Pat. No. 5,319,702, Kitchin et al., represents one system which has attempted to provide an apparatus and method for detecting the attempted placement of a three-way call by detecting a hook-flash event. Unfortunately, the apparatus is a premises-based solution and must be physically integrated with each telephone in order to function properly. As a result, the apparatus is not readily adaptable for use in a telecommunications network which would enable a single apparatus to service a plurality of telephones and a plurality of premises. In addition, the method attempts to detect a hook-flash event, in part, by identifying a pulse, present in a particular frequency band, and specific event(s) occuring after the pulse. Because the pulse may be masked by (or duplicated by) noise created along a communication path or by noise created by an individual seeking to avoid detection and because the pulse may occur within a different frequency band, the method would appear to suffer from poor reliability and would appear to have a high rate of failing to detect (or erroneously detecting) an attempted three-way call placement.
There is, therefore, a need in the industry for an apparatus and method which can more reliably detect and respond to the attempted placement of a three-way call and can solve other related and unrelated problems that become apparent upon reading and understanding this specification.